Insulated electromagnet and method of making the same



Aug. 24-, 1937. E H R N Q 2,091,234

INSULATED ELECTROMAGNET AND METHOD OF MAKING THE SAME Filed Jan. 15,1955 PIC-3.3.

Vacuum Pump Condenser ln ove Mama:

44. I Mam *4 ATTORNEY Patented Aug. 24, 1937 INSULATED ELECTROMAGNET ANDMETH- OD OF MAKING THE SAME Edward H. Branson, Rochester, N. Y.,assignor to General Railway ester, N. Y.

Signal Company, Roch- Application January 15, 1935, Serial No. 1,924

8 Claims.

This invention relates to electro-magnets and the method and apparatusfor making the same, and more particularly relates to the insulation andprotection of the windings of electro-magnets..

In railway train control apparatus and the like, certain coils, such asthe car-carried train control receiver coils, are subjected to severeshocks and vibrations and are exposed to moisture, acid, and otherdeteriorating foreign substances. It has consequently been foundexpedient to completely enclose such coils by a covering of resilientmaterial, such as vulcanized rubber, which covering is in turn protectedby a suitable coating which is resistant to acids and otherdeteriorating foreign substances.

It has been found however that the ordinary methods of vulcanizing thecovering after being applied around such coils causes the rubber toblister and often forces the rubber out at the ends of the coilsunderneath the outer protecting layer of material, and duringvulcanization of the enclosure for the coils, considerable solventvapors and moisture develop which are trapped within the windings andlater cause short-circuits and deterioration to the winding insulation.It has also been found that the covering around the coils is notuniformly vulcanized by the ordinary methods as considerable time isnecessary for the heat to penetrate to the inner .or core covering ofthe coils, which results in the outer covering being more thoroughlyvulcanized than the inner.

In view of the above and other considerations,

it is proposed in accordance with the present invention to provide anelectro-magnet as well as the apparatus for and method of making thesame which is substantially free from moisture, solvent vapors and otherdeteriorating substances, and which is also protected against subsequententrance of such substances therein. It is further proposed to providesuch apparatus for and method of vulcanizing the covering ofelectro-magnets whereby the resulting covering is uniformly vulcanizedaround both the inner and outer surfaces, and wherein the coveringmaterial is of uniform density and thickness as well as free from airpockets and blistersl Other objects; purposes and characteristicfeatures of the invention will appear as the description thereofprogresses, during whichpreferences will be made to the accompanyingdrawing which shows the invention in a manner to 55 make it easilyunderstood rather than with the view to showing the particularconstruction preferably employed in practice, and in which:-

Fig. 1 is an elevational view of a core with insulation applied theretopreparatory to the winding of the coil thereon with parts of suchinsulation broken away to more clearly show the arrangement thereof.

Fig. 2 is an enlarged sectional view showing a portion of a coil uponthe core of Fig. 1.

Fig. 3 is an elevational view of the completely covered electro-magnetpreparatory to vulcanization, with various parts thereof broken away toillustrate the arrangement thereof.

Fig. 4 is a diagrammatic and conventional view illustrating theapparatus employed in vulcanizing the covering around the coil of Fig. 3in accordance with the present invention.

Fig. 5 is an enlarged sectional view of a portion of a completedelectro-magnet constructed in accordance with the present invention.

' Referring now to the drawing, a magnetic core I is shown with a polepiece 2 attached thereto, such as by welding, or of course these partsmay be integral. This core I may be of various other shapes and of solidor laminated construction according to the'requirement, and the topportion may be adapted to retain a suitable member for holding a coilupon the body of the core I. particular core construction chosen for thepresent disclosure includes an end washer 3 of suitable rigid insulatingmaterial, which in assembly, fits over the end of the body of core I andis retained by suitable brackets 4 clamped to the opposite sides of areduced end of core I by bolts 5.

Before assembling the washers 3 and brackets 4 upon the core I however,the core I, pole piece 2 and washer 3 are all sand blasted andthoroughly cleaned with benzine, or the like, after which the bodysurface of the core I, inner surface of washer 3 and the inner surfaceof pole piece 2 are all coated with two coats of rubber priming cement,such as the typesold under the trade name of Vulculock, which isfollowed by two coats of suitable rubber cement, with a drying time ofapproximately 15 minutes allowed between each of such coats.

A large bakelite-varnish impregnated cloth ring 8 is now placed over thecore and pressed down tightly against ,the inner surface of the polepiece 2, as shown, and a smaller washer 9 of uncured rubber having anoutside diameter slightly larger than the completed coil and an insidediameter approximately equal to the di- The coil retaining means in theyameter of core I, is placed over the core I and pressed down andcemented tightly on the wash er 8. The inside diameter of the ring 8 issufficiently greater than the inside diameter of the 5 washer 9 to allowan inner circular portion of washer 9 which is within the hole in ring 8to cement to the pole piece 2. A second washer Ill of uncured rubbersimilar to the washer 9 is now pressed down and cemented tightly on the10 end washer 3, and the washer 3 together with washer I0 is now placedon the end of core I and the brackets 4 are assembled as shown inFig. 1. A sheet of uncured rubber I3 is now wrapped around the body ofcore I, which sheet of rubber I3 is to be wide enough to abut the rubberwashers 9 and I 9 and long enough so that its ends slightly overlap. Inwrapping the rubber sheet I3, the surface should be kept clean andshould be carefully ironed in place with suitable tools to eliminate allair pockets and to fit tightly against the end washers 9 and Ill. Stripsof uncured rubber (not shown) may be applied around each end of thesheet I3 in a manner to re-enforce the joints between this sheet I3 andthe rubber washers 9 and III.

In order to protect the outer portion of the rubber washers 9 and I0from dirt while winding the coil, narrow rings II of thin material suchas linen are applied to each surface of the outer portions of thesewashers 9 and I0. Two varnished cambric washers I5 having inwardlyextending flanges around their inside circumferences are placed over thecore and pressed tightly against the inner surface of the rubber washers9 and I0 respectively. In as much as it has been found expedient toassemble these washers I5 after therubber washers 9 and II) have beensealed to the core covering I3, it is necessary to cut one side of thewashers I5 thereby allowing their installation by twisting in a mannerto open this cut sufficiently to slide over the body of core I. l

A hole through a mid-portion of the end washer 3 is slightlycounter-bored, and a hole of the same size in register therewith is cutthrough both the rubber washer Ill and washer I5 to receive a flangedbushing I2 constructed of insulated material. .The outer surface of thebushing I2 is first thoroughly coated with both priming and rubbercement and a small varnished cambric washer I1 is cemented to theflanged end of bushing I2, after which the ,smaller end of bushing I2 isplaced through the holes in washers I5, I0 and 3 so that its innerflange presses the surrounding portion of washers I9 and I5 into thecounter-bored portion of washer 3 is shown in Fig. 1.

A sheet of varnish impregnated cloth I6 is now wrapped around the bodyof the core I over the rubber sleeve I3 so that its edges overlap theinner flanges of washers I5. The ends of the cloth I6 should overlapslightly and these overlapping end portions are cemented and temporarilybound with a few turns of tape until the coil is wound thereover.

In winding the coil a suitable machine of any well known type may beused and of course the size of wire and number of turns are to be chosenin accordance with the requirements of the particular application. Theinsulation on the wire used in the present coil should be impregnatedwith insulating varnish before winding. During the winding of the coil,vents or air passages are formed for conducting vapors from within thecoil to the outlet provided by the bushing I2.

These passages may be conveniently formed by inserting fibre strips 20in intermediate portions of the coil during winding thereof, the strips20 extending the full length of the coil and separating the layers ofthe winding in a manner to form voids or passages adjacent each edgethereof. One of the strips 20 is located as shown in Fig. 2 so that thevoid in the winding formed at an edge thereof aligns with the hole inthe bushing I2 '(represented by the dotted circles), and another strip20 (not shown) may be similarly located in the windings at a positiondiametrically opposite.

In winding the outer layers of wire, an annular recess, or that is, aspace having a lesser outside diameter than the center of the completedwinding, is left at each end adjacent the washers l and ID for a purposewhich will later be obvious. The method of bringing out the coil ends orleads is not herein shown in detail, but it has been found expedient tocover the beginning of the coil or the first turn with varnished cambrictubing, and in bringing this lead to the outer surface, a radial slot(not shown) may be provided in the end washer 3 into which is pressedthe rubber washer III to allow this bottom lead to be brought to theouter surface of the coil through this slot in order to prevent it frominterfering with the other turns of the coil. The outer end ispreferably terminated diametrically opposite the inner end, and flexiblerubber covered lead wires 23 may be soldered to these coil ends, whichlead wires 23 are brought around the outer top surface of the coil to acommon point as shown in Fig. 3. Y

The lead wires 23 are cleaned thoroughly and wrapped with rubber tape,after which these leads 23 and the entire outer surface of the coil arecoated with rubber priming cement and allowed to dry. A sheet of uncuredrubber 24 similar to that applied to the core I is now tightly wrappedaround the entire outer surface of the coil, beneath the extendingportion of leads 23 as shown. The ends of the sheet 24 should overlap toform a tight joint, and should be carefully ironed down with suitabletools, making sure that all air pockets are removed. In ironing down thesheet 24, the edges are rolled down into the peripheral recesses left atthe ends of the winding.

The linen protecting rings II are now removed from the rubber washers 9and I 0, and the extending portions of these washers are thoroughlycleaned and then folded inwardly over the portion of the rubber covering24 which enters the peripheral recesses and ironed down tightly in orderto knit thoroughly thereto, thus making the outer surface of the coil ofsubstantially uniform diameter throughout, as shown in Fig. 3.

The leads 23 are now placed part-way down the sides of the coil covering24, as shown, and rolls of uncured rubber are placed tightly around thesides of the leads 23, and the point at which the leads leave the coilis also carefully sealed and re-enforced by pieces of uncured rubber. Asmall square of uncured rubber 25 is placed over theleads 23 and rolleddown tightly to the coil covering 24.

The entire outer surface of the coil may now be temporarily covered withwater-soaked 'cotton tape (not shown) wound tightly thereon while wetand tied. The coil is then allowed to stand overnight, during which timethe wet tape dries to apply pressure to the rubber covering; with, theresult that the rubber covering is compressed evenly and to apredetermined dimension.

When the cotton tape has thus dried, it is removed from the coil and theextending portions of washer 8 are notched and folded inwardly over therubber coil covering. The outer surface of the coil covering is nowcoated with a suitable rubber cement followed by a cover- 10 ing ofrubberized tape 26 wound tightly over the rubber coil covering. In orderto more thoroughly compress the coil covering, water-soaked cotton tapemay again be temporarily applied in the same manner as before but overthe rubl5 berized tape 26, andthe vulcanizing of the rubber coveringshould be started while this cotton tape is still wet in order to permitthe shrinkage of the tape to compress the rubber covering against thewindings during vulcanization.

20 The apparatus required for vulcanizing the rubber covering of thecoil in accordance with the present invention includes an ovendiagrammatically represented by the dotted rectangle enclosing the coilin Fig. 4, which oven should 25 be thermostatically regulated andcapable of maintaining a temperature of 275 Fahrenheit,

with provisions included therein for conducting electrical energy froman external source into the interior thereof, and also with an externalconduit 30 arranged for conveniently connecting to the threaded hole inthe bushing I2 of the coil being vulcanized. Of course in practice anoven will be provided which will accommodate several coils at one time,and consequently a 5 manifold within the oven will bev provided andconnected suitably to the conduit 30.

A vacuum pump P is also required and is connected to the conduit 30through a suitable condenser as shown. The outlet 30 is arranged 40 tobe connected either to the vacuum pump P and condenser or to an airdrier by valves Aand B, which air drier may be of the calcium chloridetype. The interior of the oven used in vulcanizing the present coilsshould be heated to a 45 temperature of 275 Fahrenheitprior to placingthe coils therein, and while the coils are being, placed therein, thetemperature should not drop below 200 Fahrenheit.

In arranging the coils in the oven, the leads 50 23 are connected suchas by a suitable receptacle or plug connecting means to the externalelectrical circuit including an ammeter A and a switch S, wherebycurrent of a predetermined value may pass through the windings of the 55coil from an energy source, conventionally indicated by the symbols 13+and B-. The conduit 30 within the oven is also connected to the threadedbushing l2, and it is necessary to make all of these connections asquickly as possible 60 so that the temperature within the -oven does notfall below 200", otherwise the time required to again raise thetemperature to 275 will be greatly increased.

When the coil is thus arranged in the oven,

65 current is passed through the windings of a value which is found toheat the coil throughout in a period of one hour to a temperature of 275Fahrenheit. The value of this current must of course be predetermined inaccordance with 70 the total resistance and the size of wire used in thecoil.

With this current flowing in the windings of the coil, the valve A isclosed, valve B is opened and a third valve C is opened sufilciently toal- 75 low the vacuum pump P to maintain a vacuum corresponding to-anabsolute pressure of about 380 millimeters of mercury in the interior ofthe coil, while the temperature of the coil is being raised to 275. Thiscondition is maintained for approximately one hour, after which time theelectrical energy is removed from the windings of the coil by openingthe switch S, and the valve C is fully opened to raise the vacuum withinthe coil to the maximum obtainable by the pump P.

The temperature within the oven is still maintained at 275 for a secondperiod of 2 hours with the electrical energy removed from the windingsof the coil and under the maximum vacuum, after which time the oven heatis shut off and the valves B and C closed and valve A opened slowly tobreak the vacuum within the coil with dry air from the air drier. Theoven door may now be opened and with the valve A still opened the coilis allowed to cool to room temperature.

When the coil has thus cooled to room {emperature, the conduit 30 isdisconnected from the bushing l2 and the electrical connections removedfrom the leads 23. The threaded opening in the bushing l2 must now beclosed immediately, and if it is not found to be practical topermanently close this opening immediately, a temporary plug may beinserted. The method of permanently closing the opening in the bushingI2 is shown in the enlarged sectional view in Fig. 5, and consists infirst thoroughly coating the entire inner surface of the threaded holewith one coat of rubber priming cement followed by one coat of suitablerubber cement, with a drying time of approximately 10 minutes leftbetween these applications, after which, a disc of uncured rubber 32 ispressed into the hole in the bushing l2 and further forced down andretained by a threaded fibre plug 33. The temporary covering of cottontape is now removed and the coil covering is finally completed by theapplication of two coats of suitable acid-proofing paint to the entireouter surface.

It will now be seen that the process thus outlined provides a. method ofcompletely enclosing a coil by a covering 01' uncured rubber with theexception of a small vent communicating with all parts of the interiorof the coil by air passages formed during the winding thereof, therebypermitting moisture and-solvent vapors to escape from the interior ofthe coil during vulcanization. The present inventionalso provides anovel arrangement of apparatus whereby vulcanization of the coilcovering is greatly expedited by heating from within the coil' bypassing electrical current through its windings, and whereby the removalof all moisture is insured by evacuating the interior of the coil duringvulcanization, and finally the pressure within the coil covering israised to atmospheric by incoming air taken through an air drier.

The coil thus vulcanized is then completely sealed against the entranceof moisture or air by tightly and permanently plugging the vent so thatthe completed coil may then be maintained indefinitely in itsmoisture-free condition. The method and apparatus used in vulcanizingthe covering of the present coil have the further advantage of creatinga difference in air pressure between the outside and the inside of thecoil covering which results in a denser and more uniform covering ofrubber. In other words, the vacuum within the coil results in acompressive eifect of the normal air pressure on the outer surfaces, andof course, the possibilities of blistering of the coil covering due tothe building up of pressure within the coil is entirely eliminated bythe vacuum employed in the present process.

5 The above rather specific description of one form of the presentinvention is given solely by the way of example, and is not intended, inany manner whatsoever, in a limiting sense. It is also to be understoodthat various modifications,

adaptations, and alterations may be applied to meet the requirements ofpractice, without in any manner, departing from the spirit or scope ofthe present invention, except as limited by the appended claims.

What I claim is:-

1. A method of making electro-magnets, comprising, applying an innersleeve of uncured rubber to an iron core, applying end washers ofuncured rubber to the inner sleeve, providing a vent in one of the endwashers, winding a coil on the rubber spool thus formed leaving alongitudinal void in the coil aligning with the vent in the end washer,applying an outer sleeve of uncured rubber around the coil, folding theedges of the rubber washers over onto the outer sleeve, submitting thecoil thus formed to a temperature of 275 Fahrenheit for 2 hours or moreto vulcanize the rubber parts into a unitary covering, and permanentlysealing the vent in the end washer.

2. A method of making electro-magnets, comprising, applying an innersleeve of uncured rubber to an iron core, applying end washers ofuncured rubber to the inner sleeve, providing a vent in one of the endwashers, winding a coil on the rubber spool thus formed leaving alongitudinal void in the coil aligning with the vent in the end washer,applying an outer sleeve of uncured rubber around the coil, folding theedges of the rubber washers over onto the outer sleeve, passingelectrical current through the coil for one hour or more of a valueeffective to raise the temperature of the coil to 275 Fahrenheit,submitting the coil thus formed to a temperature of 275 Fahrenheit for 2hours or more to vulcanize the rubber parts into a unitary covering, andpermanently sealing the vent in the end washer.

3. A method of making electro-magnets, comprising, forming a spool ofuncured rubber, pro- 5 viding a vent in the spool, winding a coil on thespool, providing a longitudinal passage in the coil communicating withthe vent, covering the outer surface of the coil with uncured rubber soas to unite with the' edges of the spool, connecting the vent in thespool to an evacuating means,

submitting the coil still connected to the evacuating means to atemperature of 275 Fahrenheit for 2 hours or more, then breakingthevacuum within the'coil by permitting the entrance of dry air. andsealing the vent in the spool.

4. A method of making electro-magnets, comprising, forming a spool ofuncured rubber, providing a vent in the spool, winding a coil on thespool, providing a longitudinal passage in the coil communicating withthe vent, covering the outer surface of the coil with uncured rubber soas to unite with the edges of the spool, conmeeting the vent in thespool to an evacuating means, passing a value of electrical currentthrough the coil which raises the temperature throughout the interiorthereof to approximately 275 Fahrenheit, then removing the electricalcurrent and submitting the coil still connected to the evacuating meansto a temperature of 275 Fahrenheit for 2 hours or more, then breakingthe vacuum within the coil by permitting the entrance of dry air, andsealing the vent in the spool.

, the spool in a manner to completely enclose the coil except for theoutlet means, placing the coil thus covered in an oven previously heatedto approximately 275" Fahrenheit, passing electrical current through thecoil for one hour of a value which raises the temperature throughout theinterior thereof to approximately 275 Fahrenheit, then disconnecting theelectrical current and allowing the coil to remain in the oven at 275Fahrenheit for approximately 2 hours, and permanently sealing the outletmeans when the coil has cooled.

6. A method of making an electro-magnet comprising, forming a spool ofuncured rubber around an' iron core, providing an outlet means in thespool, winding a coil on the spool, providing transverse voids in theinterior of the windings of the coil communicating with the outletmeans, applying a sleeve of uncured rubber around the outer surface ofthe coil, folding the outer edges of the rubber spool over onto therubber sleeve in a manner to completely enclose the coil except for theoutlet means, placing the coil thus covered in an oven previously heatedto approximately 275 Fahrenheit, connecting a vacuum pump to the outletmeans and eiTecting a vacuum of approximately 15 inches within the coilcovering, passing current through the wind ings of the coil for one hourwith the oven temperature at 275 Fahrenheit and with the vacuum of 15inches maintained, the current being of a value effective to produce atemperature of 275 Fahrenheit throughout the interiorof the coil withinthe one hour period, then interrupting the electrical current in thecoil and increasing the vacuum therein to the maximum obtainable for aperiod of 2 hours or more with the oven temperature maintained at about275 Fahrenheit, then closing the connection from the vacuum pump to thecoil outlet means and permitting only air passing through a drying meansto enter the coil through the outlet means, and closing the outlet meansagainst the further entrance of air or other substances.

7. The process of making a moisture-free enclosed coil, consisting informing a spool of uncured rubber, winding a coil on the spool, coveringthe spool with uncured rubber so as to completely enclose the coil withthe exception of a small vent, heating the coil thus formed in a mannerto vulcanize all the rubber into a unitary covering, and completing thecoil enclosure by sealing the vent.

8. The process of making a moisture-free enclosed coil, consisting informing a spool of uncured rubber, winding a coil on the spool, coveringthe spool with uncured rubber so as to completely enclose the coil withthe exception of a small vent, evacuating the interior of the coil thuscovered through the vent, heating the coil while evacuated in a mannerto vulcanize all the rubber into a unitary covering, and completing thecoil enclosure by sealing the vent.

EDWARD H. BRANSON.

